Food web is a network of food chains or feeding relationships by which energy and nutrients are passed on from one species of living organisms to another.

At the trophic level of consumers the rate at which food energy is assimilated is called secondary productivity.Rabbit is a consumer.

Hydrarch succession takes place in wetter areas and xerarch succession respectively,which takes place in dry areas. So, both hydrarch and xerarch successions leads to medium water conditions.

It feeds upon grains hence called primary consumer and can also feed on insects hence called secondary consumer at the same time in the same ecosystem.

An energy pyramid is the graphical representation of the tropic level (nutritionals) by which the incoming solar energy is transferred into an ecosystem. It can never be inverted in shape.

A standing crop is the quantity or total weight or energy content of the organism, which are in a particular location at a particular time.

The biomass available for consumption by the herbivores and the decomposers is called net primary productivity.It is equal to the rate of organic matter created by photosynthesis minus the rate of respiration and other losses.The biomass available for consumption by the herbivores and the decomposers is called net primary productivity.It is equal to the rate of organic matter created by photosynthesis minus the rate of respiration and other losses.

The statement(a) and (b) are correct. The statement (c)is incorrect because predators cannot lead to the extinction of prey species. Predator and prey evolve together. The statement (d) is incorrect because chemical such as nicotine and strychnine produced by the plants are not metabolic disorders but are metabolic wastes.

A pond ecosystem is a delicate balance of fish, plants and other animals. Fish occupy more than one tropic level in pond ecosystem. Small fishes act as secondary consumer. They feed on primary consumer. Large fishes act as tertiary consumer. They feed on smaller fishes.

The correct sequence of plants in a hydrosere is Volvox,Hydrilla, Pistia, Scirpus, Lanatana and Oak. A hydrosere is a plant succession which occurs in a fresh water lake.In time, an area of open fresh water such as a lake will naturally dry out, ultimately becoming woodland. During this change, a range of different land types such as swamp and marsh will succeed each other. The succession from open water to climax woodland is likely to take at least two hundred years.